Commit message: irc: fix crash when receiving a malformed message 352 (who)

Thanks to Stuart Nevans Locke for reporting the issue.
CVE: CVE-2020-9759
CWE: CWE-476
Vulnerability description: A Vulnerability of LG Electronic web OS TV Emulator could allow an attacker to escalate privileges and overwrite certain files. This vulnerability is due to wrong environment setting. An attacker could exploit this vulnerability through crafted configuration files and executable files.

Project: weechat
File: irc-protocol.c

IRC_PROTOCOL_CALLBACK(352)
{
    char *pos_attr, *pos_hopcount, *pos_realname, *str_host;
    int arg_start, length;
    struct t_irc_channel *ptr_channel;
    struct t_irc_nick *ptr_nick;

    IRC_PROTOCOL_MIN_ARGS(5);

    /* silently ignore malformed 352 message (missing infos) */
    if (argc < 8)
        return WEECHAT_RC_OK;

    pos_attr = NULL;
    pos_hopcount = NULL;
    pos_realname = NULL;

    if (argc > 8)
    {
        arg_start = (strcmp (argv[8], "*") == 0) ? 9 : 8;
        if (argv[arg_start][0] == ':')
        {
            pos_attr = NULL;
            pos_hopcount = (argc > arg_start) ? argv[arg_start] + 1 : NULL;
            pos_realname = (argc > arg_start + 1) ? argv_eol[arg_start + 1] : NULL;
        }
        else
        {
            pos_attr = argv[arg_start];
            pos_hopcount = (argc > arg_start + 1) ? argv[arg_start + 1] + 1 : NULL;
            pos_realname = (argc > arg_start + 2) ? argv_eol[arg_start + 2] : NULL;
        }
    }

    ptr_channel = irc_channel_search (server, argv[3]);
    ptr_nick = (ptr_channel) ?
        irc_nick_search (server, ptr_channel, argv[7]) : NULL;

    /* update host in nick */
    if (ptr_nick)
    {
        length = strlen (argv[4]) + 1 + strlen (argv[5]) + 1;
        str_host = malloc (length);
        if (str_host)
        {
            snprintf (str_host, length, "%s@%s", argv[4], argv[5]);
            irc_nick_set_host (ptr_nick, str_host);
            free (str_host);
        }
    }

    /* update away flag in nick */
    if (ptr_channel && ptr_nick && pos_attr)
    {
        irc_nick_set_away (server, ptr_channel, ptr_nick,
                           (pos_attr[0] == 'G') ? 1 : 0);
    }

    /* update realname in nick */
    if (ptr_channel && ptr_nick && pos_realname)
    {
        if (ptr_nick->realname)
            free (ptr_nick->realname);
        if (pos_realname &&
            weechat_hashtable_has_key (server->cap_list, "extended-join"))
        {
            ptr_nick->realname = strdup (pos_realname);
        }
        else
        {
            ptr_nick->realname = NULL;
        }
    }

    /* display output of who (manual who from user) */
    if (!ptr_channel || (ptr_channel->checking_whox <= 0))
    {
        weechat_printf_date_tags (
            irc_msgbuffer_get_target_buffer (
                server, NULL, command, "who", NULL),
            date,
            irc_protocol_tags (command, "irc_numeric", NULL, NULL),
            "%s%s[%s%s%s] %s%s %s(%s%s@%s%s)%s %s%s%s%s(%s)",
            weechat_prefix ("network"),
            IRC_COLOR_CHAT_DELIMITERS,
            IRC_COLOR_CHAT_CHANNEL,
            argv[3],
            IRC_COLOR_CHAT_DELIMITERS,
            irc_nick_color_for_msg (server, 1, NULL, argv[7]),
            argv[7],
            IRC_COLOR_CHAT_DELIMITERS,
            IRC_COLOR_CHAT_HOST,
            argv[4],
            argv[5],
            IRC_COLOR_CHAT_DELIMITERS,
            IRC_COLOR_RESET,
            (pos_attr) ? pos_attr : "",
            (pos_attr) ? " " : "",
            (pos_hopcount) ? pos_hopcount : "",
            (pos_hopcount) ? " " : "",
            (pos_realname) ? pos_realname : "");
    }

    return WEECHAT_RC_OK;
}